In general, "solid-phase method" means a method for preparing a catalyst by grinding and mixing a carrier and catalyst, and then calcining this mixture. "Impregnation method" means a method for preparing a catalyst by dipping a carrier into a catalyst solution.
Chlorobenzene derivatives are widely used as a starting material or an intermediate of medicine, of agrochemistry, and in the field of organic synthesis. Up to now, they have been prepared by using Lewis acid catalysts such as ferric trichloride and antimony chloride in a liquid phase.
Dichlorobenzene derivatives produced by liquid-phase chlorination include 1,2-dichlorobenzene derivatives (o-isomer), 1,3-dichlorobenzene derivatives (m-isomer), 1,4-dichlorobenzene derivatives (p-isomer). When monochlorobenzene is chlorinated by using a Lewis acid catalyst in a liquid-phase, the proportion of isomer of dichlorobenzene is as follows;
______________________________________ o-dichlorobenzene 30-40% m-dichlorobenzene 0-5% p-dichlorobenzene 60-70% ______________________________________
A p-isomer of chlorobenzene derivatives is widely used as an important raw material and intermediate.
U.S. Pat. No. 3,029,296 and U.S. Pat. No. 3,636,171 describe, as an example of liquid-phase chlorination in the presence of a Lewis acid, a liquid-phase chlorination process for preparing dichlorobenzene by chlorinating benzene or monochlorobenzene in the presence of ferric chloride, aluminum trichloride, tin tetrachloride or titanium tetrachloride. In the above process, the ratio of para-isomer to ortho-isomer of dichlorobenzene obtained in the presence of catalyst having a mixture of aluminum trichloride and tin tetrachloride (ratio, 1:9) is 2.7 to 3.
A process of chlorination of an aromatic compound in a liquid-phase in the presence of catalyst containing cocatalyst is described in U.S. Pat. No. 4,444,583 and U.S. Pat. No. 4,235,825.
A Lewis acid catalyst has relatively high activity. However, a Lewis acid has a disadvantage in that it can not be recycled due to its dissolution into reactive solution; and thus it may cause an environmental pollution.
In order to overcome this disadvantage, a chlorination process employing a solid-acid zeolite as a heterogeneous catalyst has been tried since 1980.
An article in Tetrahendron Letters, 21, 3809 (1980) reports that benzene is chlorinated by employing catalysts of solid-acid-zeolite catalysts such as ZSM-5, ZSM-11, mordenite, L and Y; and among them, zeolite catalyst L has a high selectivity of para-dichlorobenzene.
U.S. Pat. No. 4,835,327 and U.S. Pat. No. 4,777,305 describe that a high selectivity of para-dichlorobenzene is obtained by chlorinating benzene with several types of ion-exchanged zeolite L, and that in the case of chlorination in the presence of a catalyst produced by employing multi-valent metals such as nickel and lanthanum, catalytic activity and selectivity of dichlorobenzene are slightly reduced relative to zeolite itself.
Nakamura et al, Chem. Lett., 1881 (1992) studied a liquid-phase chlorination of benzene using many kinds of solvents in the presence of zeolite L, and obtained the result that the highest para-selectivity is shown by chlorinating benzene with dichloroethane as a solvent at the temperature of 70.degree. C. in the presence of oxygen, and that oxygen gas accelerates para-selectivity in a liquid-phase chlorination of benzene.
EP 0,195,514 teaches that when impregnating an alkaline earth metal chloride (such as calcium chloride, strontium chloride and barium chloride) into NaY zeolite, potassium chloride and cesium chloride reduce both the conversion of monochlorobenzene and the para-selectivity of dichlorobenzene, while barium chloride slightly increases both the conversion and the selectivity.
The conversion rate of monochlorobenzene is increased by 4 wt % by zeolite KL, and para-selectivity of dichlorobenzene is rather reduced when using a zeolite catalyst in which 10 wt % of +3 valent-lanthanum salt is supported on zeolite KL.